1. Field of the Invention
The present invention generally relates to multiservice communications systems wherein a plurality of different services are transmitted to subscriber locations over one or more different frequency channels. More particularly, the present invention relates to methods and apparatus for providing virtual service selection in such multi-service communications systems.
2. Description of the Prior Art
Communications systems today have the ability to simultaneously transmit a multitude of video, audio, teletext and data services to subscribers. For example, with the advent of digital compression technologies, the subscription television industry has experienced an explosion in the number of services that can be provided to each subscriber. Consequently, subscribers face an overwhelming choice of available services, and providing efficient and inventive ways for subscribers to access these services is extremely important.
Most multi-service communications systems transmit different services over one or more different frequency channels. Each frequency channel may carry more than one service. Accessing a particular service requires tuning to the frequency channel carrying that service, and then selecting that service from the many services carried on that frequency channel. Generally, it is desirable to insulate subscribers from the details of service access and to allow subscribers to access different services in a like manner. Subscription television operators typically assign each service a unique number and then provide subscribers with a decoder that allows the subscriber to access a particular service by selecting that service's number using a push-button device or hand-held remote. Subscribers are thereby insulated from the complex details of service acquisition.
Additionally, it is desirable to provide system operators with the ability to easily re-assign service numbers to different services. Some services may be discontinued and others may be added, and therefore, a static numbering system rapidly becomes obsolete. Bennett et al., U.S. Pat. No. 4,908,859, and Yoneda et al., U.S. Pat. No. 5,200,823, both describe multi-service communications systems that provide system operators with a degree of flexibility in channel number assignment. Both systems employ a scheme sometimes referred to as "virtual channel mapping" in which a "channel map" is employed to map each available service to a different subscriber selectable channel number. In both systems, the channel map is stored in the user's decoder and contains an entry for each user selectable channel number. When a user selects a given service number for viewing, the decoder accesses the channel map entry for that channel number to determine which of the services being received by the decoder corresponds to the selected channel number. When the appropriate service is identified, the decoder tunes to the appropriate frequency and retrieves the selected service from the incoming data on that frequency channel. A system operator can alter the channel number assignments by modifying the appropriate channel map entries. Both systems allow a system operator to transmit new channel map entries to the decoder over one or more of the frequency channels. However, in each system, the entire channel map is stored in a memory in the decoder at all times. Unfortunately, with the ever increasing number of available services, the amount of memory required to store an entire channel map can become prohibitive. Consequently, there is a need for a method and apparatus that provides virtual service selection in a multi-service communications system without the need to store the entire channel map in the decoder. The present invention satisfies this need.